Skin Structure and Function
To better skincare and acne treatment on your face, you must first understand the skin structure and skin function on your face.
Browse the following points to give you a preliminary understanding of skin:
- The skin is a body organ, just like our facial features.
- The thickness of the skin is between 0.5 mm and 4 mm.
- Skin mass accounts for 16% of body weight.
- The pH value of the skin is generally between 4.0 and 7.0, so it is weakly acidic under normal conditions, and the continuous high pH value (Alkaline) will cause many skin problems.
- The skin has the functions of protection, sensation, regulation of body temperature, secretion, excretion, absorption, metabolism, and immunity.
The skin is really important!
In the early days, people believed that the skin was a group of inanimate cells, just a layer of dead skin standing between us and the harsh environment. The natural and fresh environment is actually very harsh. Oxygen, water mist, bacteria and tiny particles are all enemies of our cells.
But in fact, inside the skin is a factory full of firepower. From the lower layer of subcutaneous fat to the uppermost layer of stratum corneum, they are constantly working to protect our body, while also regulating body temperature (Perspiration), producing vitamin D, and feeling external stimuli. The skin and lips are very sensitive to external mechanical vibrations
The skin also conveys affection. If our skin is not good, we often just want stay at home. Good skin is conveying this message to potential friends: I am healthy, sexy, and young.
The Structure of The Skin
The structure of the skin from the inside to the outside consists of three parts: subcutaneous tissue, dermis, and epidermis. Each part has a different structure and function.
The epidermis is the outermost skin we can see.
The epidermis contains four layers: stratum basale, stratum spinosum, stratum granulosum, and stratum corneum.
The structure of the epidermis
The stratum basale is responsible for cell division and constantly provides new keratinocytes. The skin stem cells we often say are in this layer, and skin stem cells keep dividing to maintain skin renewal.
Besides, the stratum basale also contains an important cell called melanocytes. When ultraviolet rays are irradiated on the skin, the skin cells will turn to melanocytes for help. The melanocytes produce melanin to resist the damage of ultraviolet rays.
Stratum spinosum, stratum granulosum:
These two layers are located in the middle of the epidermis. The stratum spinosum is involved in repairing damage to the epidermis, and the stratum granulosum is involved in filtering ultraviolet rays and retaining moisture.
The water content of the stratum corneum decreases rapidly, the water content drops from 80% to below 20%, and the vital activities of cells are also greatly reduced. However, the stratum corneum is flexible and dense, and the stratum corneum can withstand daily friction and pressure, which acts as a skin barrier. The stratum corneum protects the other skin structures underneath to work normally.
The surface of the stratum corneum is covered with sebum secreted from the sebaceous glands. The sebum membrane is the collection of sebaceous oil, sweat, and dead cells from the sebaceous glands. Sebum is the first protective layer of the skin. Sebum prevents moisture loss and keeps the skin supple.
The stratum corneum is made up of keratinocytes that are tightly attached. The keratinocytes contain a large amount of water-absorbing keratin and natural moisturizing factor (NMF).
The keratinocytes are filled with lipids that are tough and do not penetrate easily.
If the stratum corneum is likened to a dam against water loss, then the keratinocytes are bricks and the lipids are cement.
The metabolic cycle of the epidermal layer of healthy skin:
- Newborn epidermal cells divide and multiply in the stratum basale until they begin to keratinize (Metabolism) = 12-19 days.
- Epidermal cells gradually move outward from the stratum basale, and the period of reaching the stratum corneum = about 14 days.
- The dead keratinocytes accumulate in the stratum corneum until they fall off = about 14 days.
- Cuticle renewal cycle = 28 days.
Below the epidermis is the dermis, the dermis is composed of two major fibers.
- One is collagen fiber, its main component is collagen, which is tough and soft. Collagen is a storehouse of moisture in the dermis. The water content of the dermis accounts for 60% of all skin.
- The second is elastic fiber, its main component is elastin, which is very elastic
Collagen fibers and elastic fibers cross to form an elastic net, which is like a spring in a spring bed, maintaining the elasticity and tension of the skin. If both of these fibers are healthy, the skin will be elastic and firm.
If the dermis is damaged by ultraviolet rays and other factors, the spring will become inelastic or broken, and the skin will become loose, wrinkled, and aging.
Besides, there are many important accessory functional structures in the dermis, including sebaceous glands, sweat glands, and capillaries.
Sebaceous glands are found in hair-covered areas, where they are connected to hair follicles.
The main function of sebaceous glands is to secrete sebum, which spreads on the surface of the skin to moisturize the skin and hair, prevent dryness of the skin, and make the skin smooth, shiny and soft.
Sebum contains fatty acids, which makes the skin pH is acidic and also has a bactericidal effect.
In short, the sebaceous glands are where the skin produces oil. It is the main factor that causes people to look shiny.
The ducts of sweat glands are thinner, distributed from the deep dermis to the skin surface. The ducts of the sweat glands open up spirally after entering the epidermis, leading directly to the sweat holes on the skin surface.
Sweat secretion is the main way for the body to dissipate heat. When the body temperature is too high, which may threaten the normal operation of body functions, the sweat glands begin to perspire, and the sweat evaporates to take away the body’s heat and achieve the effect of lowering body temperature.
In short, sweat glands are where the skin sweats.
The capillary vessels connect arteries and veins, and the walls of the vessels are usually composed of a single layer of cells. The capillaries can be considered as the energy supply station that blood provides to the skin, supplying essential nutrients and oxygen to the skin.
The structure of hypodermis
The hypodermis is located in the lowest layer of the skin structure. The subcutaneous tissue is composed of loose connective tissue and fat.
The hypodermis is an important part of supporting the skin because the shape and distribution of subcutaneous fat largely determine the contour of the skin. The subcutaneous tissue largely determines the shape of your face.
Hypodermis also has the functions of buffering mechanical pressure, storing energy, and keeping warm. This means that you will have more anti-hit, anti-hungry, and anti-freeze skills than before.
At the same time, the hypodermis also provides the energy support necessary for life for the entire skin (The epidermis and dermis). The hypodermis contains blood vessels (Arteries and veins) and subcutaneous fat. The blood is transferred from the heart to bring fresh oxygen and nutrients, and then the blood flows back to the heart through the veins, taking away waste products metabolized by cells and exhaled carbon dioxide.
Subcutaneous fat can also store energy and heat insulation.
There are hair follicles hidden in the hypodermis, and the hair grows outward from here.
The Function of The Skin
1. Barrier function:
Protect the subcutaneous organs and tissues of the human body from the damage of the external environment, such as mechanical, chemical, and other harmful factors, and prevent the loss of various nutrients, electrolytes, and water in the tissues.
Healthy skin has two barrier functions. One is to prevent damage from the outside world, and the other is to prevent the loss of nutrients, electrolytes, and moisture in the body.
The skin is like a city wall, protecting the subcutaneous organs and tissues to work safely, resisting various attacks from the external environment, such as:
- Mechanical damage, such as impact.
- For chemical damage, the prevention of this type of damage mainly relies on the stratum corneum, followed by the buffering capacity of the hydrogen ions on the skin to acid and alkali.
- Biological damage refers to microorganisms, they can become pathogenic bacteria and cause harm to the human body under certain conditions.
For example, if we take a bath for an hour, and most of our skin does not feel swollen, this is the function of the skin’s barrier to prevent moisture loss.
2. Sensory function:
The sensory nerve endings of healthy skin can transmit six senses: touch, pain, cold, temperature, pressure, and itching.
In addition to these six single sensations, there is also a sensation category called compound sensations, such as wet, dry, smooth, and soft.
3. UV protection function:
Melanin can determine skin color and prevent harmful ultraviolet rays from damaging cells. It is produced by melanocytes located in the stratum basale. The produced melanin is stored in melanocytes and is sent to surrounding epidermal cells through the protrusions of melanocytes. With the metabolism, the melanin is sent to the surface of the skin and finally shed along with the dead cells.
Melanin includes black eumelanin and yellow pheomelanin, and the ratio of these two melanins determines a person’s skin color. In addition, under the influence of strong ultraviolet rays and hormones, melanocytes will become active and constantly produce melanin. After the excess melanin is deposited, colour spots are formed.
4. The function of regulating body temperature:
Humans are warm-blooded animals and naturally have a perfect temperature regulation mechanism.
In hot weather, the temperature is high, the blood flow of the skin increases, and more heat is carried from the inside of the body to the surface of the body. A lot of heat can also be eliminated by perspiration because the evaporation of sweat requires heat.
In cold weather, the temperature is low, the metabolism in the body is enhanced to produce heat. At the same time, the capillaries inside the skin shrink, and blood flow are reduced. Together with the protection of the surface sebum film and subcutaneous fat, the body temperature is maintained.
5. Absorption function:
The skin can absorb external substances. This absorption is accomplished through the stratum corneum, hair follicles, sebaceous glands, and sweat glands. This kind of absorption is indispensable for maintaining health, and it is also the theoretical basis for the treatment of skin diseases with topical drugs in modern dermatology.
6. Secretion and excretion function:
The skin has a certain secretion and excretion function, which is mainly carried out by the sweat glands secreting sweat and the sebaceous glands excreting sebum. Perspiration also has a heat dissipation function.
7. Metabolism function:
A cycle of skin metabolism is 28 days. In each cycle, cells in the stratum basale will gradually move up to the surface of the skin and finally fall off, while taking away waste products in the skin.
8. Immune Function:
The skin is the first line of defense for human beings against harmful substances in the external environment. For a long time, people only thought that the skin was only an external barrier for the human body, and played little role in the immune response.
After in-depth research, people discovered that the skin has strong non-specific immune defense capabilities and very important specific immune functions, and it is a unique immune organ.